Monitor circuit for combustion-powered sound source



Oct. 20, 1970 3 c p 3,535,587

MONITOR CIRCUIT FOR COMBUSTION-POWERED SOUND SOURCE,

Filed March 22, 1968 M/ VE/V TOR I oyz'fmw Z5 Wcafaz'n AGENT 1 United States Patent Oifice 3,535,587 Patented Oct. 20, 1970 3,535,587 MONITOR CIRCUIT FOR COMBUSTION- POWERED SOUND SOURCE Silvan E. McAlpin, Dallas, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Mar. 22, 1968, Ser. No. 715,258 Int. Cl. H05b 37/00 US Cl. 315-119 4 Claims ABSTRACT OF THE DISCLOSURE The specification discloses a monitor circuit for the glow plug energizing circuit of a diesel fuel-powered sound source. A rectifier circuit senses the current in the energizing circuit by means of a current transformer and generates a rectified output proportional to this current. A meter relay circuit responds to levels of the rectified output below a preset minimum or above a preset maximum to cause a power relay to remove energizing power from the glow plug energizing circuit upon the occurrence of either condition.

BACKGROUND OF THE INVENTION Nondynamite sound sources have gained widespread use in seismic exploration, oceanography, and other fields. Some of these sources such as the one described in pending applications Ser. No. 534,130, filed Mar. 14, 1967 now Pat. No. 3,397,755, and Ser. No. 663,663, filed Aug. 28, 1967 now Pat. No. 3,434,561, both by George B. Loper, employ combustion to produce a high pressure. A mixture of diesel fuel and air is ignited in a closed chamber, and then the resulting products of combustion are suddenly released to generate a sharp sonic pulse. The operation is repeated cyclically to generate a succession of sonic pulses.

Glow plugs in the combustion-type source, used to ignite the fuel mixture, ordinarily require a high power energizing circuit which may carry current on the order of 80 amperes. The energizing current is carried by long supply cables which are subject to such bending and stress as to cause frequent short circuits. If a short circuit occurs in the energizing circuit, the short circuit current may cause the conductors in the supply cable to become welded together and otherwise cause great damage to the equipment associated with the sound source If one of the glow plugs fails, thus reducing the effective ignition capability, it may be important to notice this fact so that the glow plug may be replaced.

In the past, it was necessary to have a man monitor the current in the energizing circuit by means of an ammeter to check for undercurrents or overcurrents. But even so, it was sometimes impossible for this man to remove power quickly enough to prevent damage upon short circuit in the glow plug energizing circuit.

Ordinary circuit breakers are not capable of providing circuit protection for both under and over current in the ignition energizing circuit with sufficient precision and quickness of operation. Nor are the trip levels of ordinary circuit breakers easily adjustable over a wide range.

SUMMARY OF THE INVENTION This invention provides a novel monitor circuit which automatically monitors the condition of the energizing circuit supplying the ignition means or glow plugs of a combustion-powered sound source. This monitor circuit provides both over and under current interruption within a manually adjustable range. If the current in the energizing circuit exceeds a maximum set point or trip level for any reason such as due to a short circuit, the monitor circuit automatically removes power from the energizing circuit. Likewise, if the current in the energizing circuit falls below a preset minimum level such as due to failure of one or more of the ignition means in the sound source, the monitor circuit also removes the power from the energizing circuit. The maximum and minimum trip levels may be set at any value to give an acceptable range of operation for the current in the energizing circuit.

Thus, this monitor circuit eliminates the manpower required to observe the condition of the energizing circuit and provides automatic circuit interruption for over or undercurrents.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic illustration of a combustionpowered sound source suspended from a boat during seismic exploration.

FIG. 2 is a schematic diagram of the monitor circuit of the present invention in initial condition before power is applied to the glow plugs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, there is illustrated a series of ignition means or glow plugs 10 which are physically located inside the combustion chamber of sound source 12 suspended behind boat 14. The energizing circuit supply cables for glow plugs 10 are shown schematically as conductors 20.

The energizing circuit for glow plugs 10 includes a source of ACpower applied to terminals 15a and 15b. The AC power appearing at terminals 15a and 15b is applied to a step-down transformer 18. The reduced voltage appearing at the secondary of transformer 18 is applied via conductors 20 to the glow plugs 10, which are shown connected in parallel with each other. A circuit breaker 22 provides protection on the primary side of transformer 18 against high overcurrent levels. Adjustment of switch 24 to various taps along the primary of transformer 18 provides different levels of voltage to the conductors 20 supplying the glow plugs 10.

In one embodiment of the monitor circuit in actual use, a llO-volt AC supply is connected to terminals 15a and 15b and switch 24 is adjusted to a tap required to produce about 16 volts RMS across conductors 20 at the secondary of transformer 18. In this same embodiment the conductors 20 carry a current of about amperes under normal operation with each of the glow plugs 10 functioning properly.

The monitor circuit illustrated in FIG. 2 is shown under the initial start-up conditions before AC power is applied to conductors 20. The monitor circuit includes a power relay 26, a current transformer 30, a rectifier circuit 34, and a meter relay circuit 40. Power relay 26 is shown in its energized condition such that its contacts remove power from glow plugs 10. The primary of current transformer 30 is shown connected in series circuit with conductors 20. Connected across the secondary of current transformer 30 is a variable resistor 32. Rectifier circuit 34 is shown as a diode bridge rectifier coupled to the secondary of transformer 30. Capacitor 38 connected across the output of rectifier 34 smooths the pulsating output of rectifier 34 to a substantially constant DC level. The values of resistor 36 and capacitor 38 and the adjustment of resistor 32 are such that a direct current is produced through resistor 36 and meter relay circuit 40 which is directly proportional to the current flowing in conductors 20.

The meter relay circuit 40, which is a commercially available device, includes a DC meter 42 which is calibrated to read the current flowing in conductors 20. Meter relay circuit 40 also includes an adjustable maximum set point illustrated diagrammatically at 44 and an adjustable minimum set point illustrated diagrammatically at 46. When the current flowing through meter 42 falls below the minimum set point 46, the relay circuit 40 opens switch 60 to produce a condition which causes power relay 26 to become energized and removes AC power from the glow plugs. Likewise, when the current 4 flowing through meter 42 rises above the maximum set point 44, the meter relay circuit 40 opens switch 70 to produce a condition which causes power relay 26 to become energized and remove AC power from the glow plugs. Both the minimum and maximum set points 46 and 44 are manually adjustable to provide any desired range of operating conditions for the current in conductors 20.

START-UP CONDITION Consider now the operation of the monitor circuit under initial conditions when no power is being applied to conductors 20. Power relay 26 is maintained energized by a supply circuit traced from the AC power at terminals a through switch 48, coil of relay 26, relay contacts 50a or 52b, and back to terminals 15b. Relay contacts 50a and 52b provide alternative paths for the energization of relay 26.

At the time start-up is desired, push button switch 48 is depressed to break the circuit across terminals 48a and 48b and thereby de-energize relay 26 so that its contacts move to the uppermost position and AC power is applied to glow plugs 10. When push button switch 48 moves to contact terminals 480 and 48d, a circuit is completed to apply DC voltage from a power supply connected to terminals 51a and 51b to energize the coil of relay 52. As the relay contact 52a moves to its lowermost position, a latch for the relay coil is picked up from the DC voltage at terminals 51a and 51b. When the current in conductors increases above a value corresponding to the minimum set point 46, meter relay circuit causes closure of a switch 60. Closure of switch applies the DC voltage from a power supply connected to terminals 61a and 61b to energize the coil of relay 50, thereby moving its contacts 50a to the lowermost position. With relays 50 and 52 energized, both paths in the supply circuit for power relay 26 are broken, i.e., relay contacts 50a and 52b are open. Thus, when push button switch 48 is released to contact terminals 48a and 48b, power relay 26 remains unenergized, and power is continually applied to the glow plugs.

UNDERCURRENT CONDITION Now assume that a condition occurs in the energizing circuit of glow plugs 10 that causes a reduction in current below the minimum set point 46. At this moment the meter relay circuit 40 opens switch 60, thereby deenergizing the coil of relay 50 and returning relay contacts 50a to the uppermost position. Power relay 26 is then energized from the AC source connected to terminals 15a and 15b and power is removed from the glow plugs.

OVERCURRENT CONDITION If a condition occurs in the energizing circuit for glow plugs 10 to cause an overcurrent above the maximum set point 44, such as when a short circuit occurs, the meter relay circuit 40 opens switch 70, thereby removing holding current from the coil of relay 52. When the relay contact 52b moves to its uppermost position, the supply circuit for power relay 26 is completed to energize relay 26 and thereby remove AC power from the glow plugs. This supply circuit may be traced from terminal 15a through switch 48, coil of relay 26, contacts 52b, and thence to terminal 15b.

In one successfully operating installation of the monitor circuit of the present invention, the following component values and types were used:

Component: Value or type Current transformer 30 Flexiformer TP-lSO. Resistor 32 ohms wirewound set at 55 ohms. Diodes in bridge rectifier 34 1 N400'3.

Capacitor 38 100 mfd. Resistor 36 11.2 kohms. Meter relay circuit 40 Simpson double set point meter relay controller, w i t h g 0-1 ma. DC ammeter. Power relay 26 P o tt e r Brumfield PM17AY.

It will be recognized that in other embodiments of the invention that power relay 26 can be in the unenergized condition to remove power from the glow plugs. In such case, the meter relay circuit would condition the energizing supply circuit for relay 26 to de-energize the relay 26 upon the occurrence of an over or under current condition.

Now that one embodiment of the invention has been described, those skilled in the art may imagine still other embodiments within the true spirit and scope of the invention. It is intended to cover all such embodiments as fall within the scope of the appended claims.

The invention claimed is:

1. A monitor circuit for a combustion-powered sound source, comprising in combination with a fuel ignition means supplied by an AC energizing circuit:

(a) a current transformer connected in series with said energizing circuit;

(b) a rectifier circuit coupled to said current transformer for developing a rectified output proportional to the current in said energizing circuit;

(c) a power relay having contacts in said energizing circuit;

(d) a supply circuit for supplying energizing current to said power relay; and

(e) a meter relay circuit coupled to said rectifier circuit and said supply circuit and having an adjustable maximum set point, said meter relay circuit being responsive to levels of said rectified output above said maximum set point to condition said supply circuit to change the state of said power relay, thereby removing power from said ignition means.

2. The monitor circuit defined by claim 1 wherein:

said power relay is connected in said energizing circuit such that power is removed from said energizing circircuit when said power relay is energized; and

said meter relay circuit conditions said supply circuit to energize said power relay when said rectified output exceeds said maximum set point.

3. The monitor circuit defined by claim 1 wherein:

said meter relay circuit further includes an adjustable minimum set point; and

said meter relay circuit is responsive to levels of said rectified output below said minimum set point to condition said supply circuit to change the state of said 5 power relay, thereby removing power from said ig-' nition means. 4. The monitor circuit defined by claim 3 further including a manually actuated switch connected in said supply circuit whereby actuation of said switch will prevent said supply circuit from causing said power relay to remove power from said ignition means under initial starting conditions before said rectified output exceeds said minimum set point.

6 References Cited UNITED STATES PATENTS 3,054,991 9/1962 Howell 340251 JOHN W. HUCKERT, Primary Examiner R. F. POLISSACK, Assistant Examiner US. Cl. X.R. 

